The present invention relates to a curable composition containing two or more curable polymers. More specifically, it relates to a curable composition that contains an acrylic acid ester and/or methacrylic acid ester based curable polymer, and a curable oxyalkylene polymer, and which has superior mechanical properties, transparency, storage stability and weather resistance. In the following description, an acrylic acid ester and/or methacrylic acid ester is referred to as a (meth)acrylic acid ester.
The present inventors previously found that a (meth)acrylic acid ester based polymer having silicon-containing functional groups that are capable of crosslinking by forming siloxane bonds either at terminals or in side chains (this type of silicon-containing functional groups is hereinafter referred to as reactive silicon functional groups) crosslinks at normal temperatures by reacting with moisture, particularly the moisture in the air, to form a network structure, thereby yielding a cured product having good properties such as high weather resistance, hardness and water resistance. The present inventors accomplished an invention based on this finding and filed a Japanese patent application (OPI) No. 36395/79 (hereinafter OPI is referred to as unexamined published Japanese patent application).
Oxyalkylene polymers having reactive silicon functional groups have been proposed in many patents such as Japanese Patent Publication Nos. 36319/70, 12154/71, 32673/74, and Japanese Patent Application (OPI) Nos. 156599/75, 73561/76, 6096/79, 82123/80, 123620/80, 125121/80, 131022/80, 135135/80 and 137129/80.
The prior art (meth)acrylic acid ester based polymers containing reactive silicon functional groups have superior performance but, on the other hand, the cured products thereof are brittle and even with resin compositions having low glass transition points, the cured products have unacceptable physical properties such as low tensile strength and low percent elongation at break.
The cured products of oxyalkylene polymers having reactive silicon functional groups possess better tensile characteristics but there still is the need to achieve further improvements in their characteristics. In addition, all of the known oxyalkylene polymers having reactive silicon functional groups are defective in their performance in that because of the structure of the backbone chains and other factors, they do not possess satisfactory weather resistance and fail to produce adequate bond to various substrates.
Several methods have been proposed as techniques that are capable of eliminating the defects of the prior art oxyalkylene polymers having reactive silicon functional groups. In the method disclosed in U.S. Pat. No. 4,593,068, an oxyalkylene polymer having reactive silicon functional groups are blended with a (meth)acrylic acid ester based polymer optionally having reactive silicon functional groups. This method is effective to some extent for the purpose of improving the initial performance of the oxyalkylene polymer having reactive silicon functional groups but it is not easy to obtain sufficiently compatible composition having good transparency and good storage stability.
Methods are also known in which (meth)acrylic acid ester based monomers are modified by being polymerized in the presence of oxyalkylene polymers having reactive silicon functional groups (see U.S. Ser. No. 759,877, and U.S. Pat. No. 4,618,656 and 4,618,653). These methods are capable of improving properties such as storage stability but they suffer from the disadvantage of reduced production rate, in particular, low production rate per the capacity of the polymerization vessel since the product obtained by preliminary polymerization and reaction must be charged into another polymerization vessel for performing the polymerization of the necessary monomers. Furthermore, if one wants to make a modified oxyalkylene polymer having a different monomer/oxyalkylene polymer ratio, it is necessary to perform polymerization in the presence of the oxyalkylene polymer each time such need arises, which is quite troublesome. It has therefore been desired to attain the intended results by mere blending.